fix to issue 1029 - we were unable to drop database if it was already in use

Fix is to apply "ALTER DATABASE ... SET SINGLE_USER WITH ROLLBACK IMMEDIATE" before trying to drop the database. This only applies to (non-Azure) SqlServer.

Sql Azure will drop the database even if it's in use, and I verified that the command is supported on SqlServer 2008 and above.
Any reason to not just do this in the SQL generator for DropDatabaseOperation?